1. Field of the Invention
The present invention relates to a pneumatic tire. More specifically, the present invention relates to a pneumatic tire having an inner liner that is configured to improve durability of the pneumatic tire.
2. Background Information
In recent years, it has been proposed to use a film mainly made of a thermoplastic resin as an inner liner for a pneumatic tire as described, for example, in Japanese patent application Kokai publication No. 2009-241855. For actual use of such a film, a manufacturing method is generally employed in which the laminated sheet including the film and a tie rubber sheet cured and adhered to the film are wound around a tire making drum and lap-spliced and are then subjected to a step of cure-molding the tire.
Alternatively, a tire can be manufactured by pulling out and cutting the laminated sheet, which includes the film mainly made of the thermoplastic resin and the tie rubber sheet and which has been wound into a roll-shaped body, from the roll-shaped body by a desired length, and winding the laminated sheet around the tire making drum. The process further includes lap-splicing the laminated sheet on the drum or the like, and then cure-molding the laminated sheet. In this case, after the tire starts to be used for running, delamination may occur between the film mainly made of the thermoplastic resin, which constitutes the inner liner, and the tie rubber sheet that has been cured and adhered to the film.
To further illustrate this, as shown in FIG. 5(a), a laminated sheet 1 including a film 2 mainly made of a thermoplastic resin and a tie rubber layer 3 is cut into a predetermined size (length) with an edge tool or the like. Then, both end portions of the laminated sheet 1 are overlapped with each other and lap-spliced on a tire making drum in such a way that a lap-splice portion S is provided and the laminated sheet 1 forms an annular shape. When one laminated sheet 1 is used, both end portions thereof are lap-spliced in such a way that laminated sheet 1 forms an annular shape. Meanwhile, when a plurality of laminated sheets 1 are used, corresponding end portions of the laminated sheets 1 are lap-spliced and joined together in such a way that the laminated sheets 1 form one annular shape as a whole.
Then, other parts (not illustrated) necessary for manufacturing the tire are wound and cure-molding is performed with a bladder. As a result of the cure-molding, the film 2 mainly made of the thermoplastic resin forms an inner liner layer 10 as shown in the view in FIG. 5(b) as a model. Around the lap-splice portion S, there are formed a portion where the film 2 mainly made of the thermoplastic resin is exposed and a portion where the film 2 is embedded in the tie rubber layer. That is, in FIGS. 5(a) and 5(b), an upper side is a tire inner cavity side. In other words, there is formed a pneumatic tire T which has the lap-splice portion S where the end portions of the film 2 in the tire circumferential direction overlap each other in the tire widthwise direction with the tie rubber therebetween and in which the lap-splice portion S exists extending in the tire widthwise direction.
The phenomenon of delamination between the aforementioned film 2 mainly made of the thermoplastic resin and the tie rubber sheet 3 cured and adhered to the film 2 occurs particularly in a vicinity 4 of the tip or the like of the film 2 at a spot shown in FIG. 5(b) where the film 2 mainly made of the thermoplastic resin is exposed. In the beginning, a crack develops, and then grows into the sheet delamination phenomenon.